I'm sure you have tried at least some of this, but like the others, it brings back memories for me. I remember changing a hydralic clutch pedal master cyclinder on some rice burner my new (at the time) wife had, and also trying to bleed the brakes on a VW rabbit. (You have to jack the rear or it will never work.) It snowed the whole time for both of those jobs.

Start with lots of layers of clothing, of course. Thermal underwear is your friend. I would not recommend using a heater unless absolutely necessary. Put up a wind block of some sort to block any wind. Drink coffee, and move around a lot, don't lie still too long (shouldn't be a problem). Take a break every 30-45 minutes and go inside and warm up for 5 minutes or so. With all the coffee you will be drinking, going inside every 30 minutes shouldn't be a problem, either. :-)

Good luck.